The role of the nervous system in growth and differentiation of its target organs is well documented. It has been implicated in the induction of limb regeneration in salamanders and young opossum. We have been studying such inductive functions in the chick embryo, and have correlated the regeneration of new limb segments with the increase in the nerve supply to the amputated stumps provided by the implanted neural tube. The questions concerning embryonic age and type of neural implant, and more importantly, the mechanism of action have yet to be addressed. To this end, we intend to: (1) investigate the daily changes that occur in regeneration of the limb as a consequence of neural induction, (2) define the age and source of embryonic implant that produce new limb segments, and determine whether the age of the host is critical, (3) identify the contribution of the fibers derived from the implant in the regenerated segments by using specific tracers, and (4) determine whether a constant infusion of soluble growth substances can induce a regenerative response. Acquisition of such information will aid us in determining the mechanism of action of implanted nerve tissue on limb regeneration.